Comme l'indiquent les divergences observées dans la littérature, la question de l'existence d'une modification du contrôle proprioceptif du mouvement au cours du vieillissement physiologique de l'adulte fait encore débat. Pour mieux comprendre ces divergences, trois études ont été réalisées afin de tester les effets de contraintes d'origines musculaire, attentionnelle et temporelle sur le contrôle proprioceptif du mouvement. La tâche commune à ces trois études était une tâche d'estimation active directe controlatérale de la position de la cheville. Les effets de contraintes musculaire, cognitive et temporelle sur les performances de contrôle proprioceptif ont été respectivement testés dans les conditions de fatigue et non fatigue, de simple et double tâche, et de vitesses libre et rapide. Pour évaluer la performance de contrôle proprioceptif, les erreurs totale, variable et constante ainsi que des variables temporelles et cinématiques ont été analysées. Chez les participants jeunes, les résultats de la première étude ont montré que la fatigue musculaire altère la performance d'estimation de position lorsque la cheville de référence est maintenue activement en position mais pas lorsqu'elle est maintenue passivement. Afin d’éviter de confondre un effet de la fatigue musculaire éventuellement induite par la répétition de la tâche d'estimation de position, les deuxième et troisième études ont été réalisées avec la référence maintenue passivement en position. Les résultats de ces deux études ont montré qu'en l'absence de contraintes cognitive et temporelle, la performance de positionnement final dans la tâche proprioceptive est comparable entre les adultes jeunes et âgés. Cependant, la stratégie utilisée pour atteindre cette position est différente selon l'âge. Les résultats ont également montré que l'adjonction d'une contrainte cognitive ou temporelle produit une dégradation de la performance de contrôle proprioceptif des adultes âgés par rapport aux adultes jeunes. Dans l’ensemble, ces résultats montrent que la capacité des adultes âgés à résoudre les problèmes posés par les contraintes environnementales est inférieure à celle des adultes jeunes et mettent en évidence la modification de contrôle proprioceptif du mouvement qui s'opère au cours du vieillissement physiologique. / As outlined by strong and unexplained discrepancies in the literature, whether proprioceptive control of movement is altered in physiological adult ageing is still under debate. In an attempt to unify these previous results, the three studies of the present thesis proposed to test the effects of muscle, attentional and temporal stresses on the proprioceptive control of movement, respectively. The common task of these three studies was an ankle contralateral concurrent matching task. To test the effects of muscle, cognitive and temporal stresses on the proprioceptive control performance of older and young adults, participants performed the matching task in fatigue and no-fatigue, single and dual task, and self-paced and fast speed conditions, respectively. To assess participants' proprioceptive performance, error, temporal and kinematic variables were analysed. The results of the first study showed that performance in the matching task was altered by muscle fatigue only when the reference was actively maintained. To avoid confounding fatigue effects with other effects, the second and third studies assessed the matching task with a reference passively maintained. The results of these studies first showed that end-point performance in the matching task was similar in young and older adults in the absence of cognitive and temporal stress. However, the strategies the participants used to reach the end-point position were different in young and older adults. Second, the addition of a cognitive or temporal stress degraded the proprioceptive control performance in older adults as compared to the young ones. Taken together, these results emphasize a decreased resilience to stressors in older adults as compared to young ones and highlight the age-related alteration in proprioceptive control of movement.

La latence, c'est-à-dire le délai entre l'action d'un utilisateur en entrée d'un système et la réponse correspondante fournie par le système, est un problème majeur pour l'utilisabilité des dispositifs interactifs. La latence est particulièrement perceptible pour l’interaction au toucher et détériore la performance de l'utilisateur même à des niveaux de l'ordre de la dizaine de millisecondes. Or, la latence des écrans tactiles actuels (smartphones ou tablettes) est en général supérieure à 70 ms.Notre objectif est d'améliorer nos connaissances sur la latence (ses causes, ses effets) et de trouver des méthodes pour la compenser ou en diminuer les effets négatifs. Nous proposons un état de l'art des travaux en IHM sur le sujet, puis nous effectuons un rapprochement avec la littérature du contrôle moteur qui a aussi étudié le comportement humain face à des perturbations visuomotrices et en particulier l’adaptation des mouvements à un retard du retour visuel.Nous détaillons ensuite nos quatre contributions. Nos résultats contribuent de manière à la fois pratique et théorique à la résolution du problème de la latence lors de l'interaction au toucher direct. Deux contributions complètent le diagnostic de la latence : la première est une nouvelle technique de mesure de latence; la seconde est une étude de l'effet de la latence sur l'interaction bimanuelle, importante pour l'interaction sur les grandes surfaces tactiles. Nous montrons que l'interaction bimanuelle est autant touchée par la latence que l'interaction à une main, ce qui suggère que des tâches plus complexes, qui augmenterait la charge cognitive, ne réduisent pas nécessairement l'effet de la latence. Nos deux autres contributions portent sur la réduction des effets de la latence. D'une part, nous proposons un système à faible latence (25 ms) associé à une compensation prédictive logicielle, et nous mettons en évidence que ce système permet d'améliorer la performance des utilisateurs comme s'ils utilisaient un système à 9 ms de latence. D'autre part nous étudions la capacité des utilisateurs à s'adapter à la latence pour améliorer leur performance sur une tâche de suivi de cible et nous montrons que l'impact négatif de la latence se réduit sur le long terme grâce aux capacités d'adaptation humaine. / Latency, the delay between a user input on a system and the corresponding response from the system, is a major issue for the usability of interactive systems. In direct-touch interaction, latency is particularly perceivable and alters user performance even at levels in the order of ten milliseconds. Yet, current touch devices such as smartphones or tablet-pc exhibit in general latencies over 70 ms.Our goal is to improve the knowledge on latency (its causes, its effects) and to find strategies to compensate it or to decrease its negative effects. We present a review of the HCI literature on the topic, then we link this literature with the motor control research field that has studied human behaviour when facing visuomotor perturbations, and in particular the adaptation to feedback delay.We then present our four contributions. We contribute both in a practical and a theoretical manner to the problem of latency in direct-touch interaction. Two of our contributions supplement the diagnosis of latency: the first one is a new latency measurement technique; the second one is a study of the impact of latency on bimanual interaction, which is important when interacting on large tactile surfaces. We show that bimanual interaction is as much affected by latency as a single hand interaction, suggesting that more complex tasks, suppose to increase the cognitive load, do not necessarily reduce the effect of latency. Our two other contributions address the reduction of the effects of latency. On one hand, we introduce a low latency system (25 ms) associated with a predictive software compensation, and we show that the system enables users to improve their performances as if they were using a system with 9 ms of latency. On the other hand we study users' ability to adapt to latency in order to improve their performance on a tracking task, and we show that the negative impact of latency is reduced with long-term training thanks to human adaptability.

abstract: The current paper presents two studies that examine how asymmetries during interpersonal coordination are compensated for. It was predicted that destabilizing effects of asymmetries are stabilized through the recruitment and suppression of motor degrees-of-freedom (df). Experiment 1 examined this effect by having participants coordinate line movements of different orientations. Greater differences in asymmetries between participants yielded greater spatial deviation, resulting in the recruitment of df. Experiment 2 examined whether coordination of movements asymmetrical in shape (circle and line) yield simultaneous recruitment and suppression of df. This experiment also tested whether the initial stability of the performed movement alters the amount of change in df. Results showed that changes in df were exhibited as circles decreasing in circularity and lines increasing in circularity. Further, more changes in df were found circular (suppression) compared to line (recruitment) movements. / Dissertation/Thesis / M.A. Psychology 2013

O presente estudo teve como objetivo avaliar o efeito da expectativa na reorganização de aspectos espaciais e temporais em ações interceptativas. O estudo foi conduzido em dois experimentos, nos quais os participantes interceptaram manualmente um alvo móvel virtual em situações com diferentes probabilidades de mudança de trajetória/velocidade de deslocamento do alvo. Em ambos os experimentos foi realizada a comparação entre um grupo que recebeu informação verbal sobre a probabilidade de mudança de trajetória/velocidade (PR), e outro que não recebeu informação (SI) sobre as características probabilísticas da tarefa. Os resultados do experimento com mudança de trajetória indicaram que, além da reorganização na dimensão espacial ocorrer de maneira gradativa, as ações interceptativas parecem ter sido controladas por um mecanismo preditivo que é atualizado ao longo do tempo por informação visual. Em ambos os experimentos foi mostrado que a probabilidade do contexto influenciou as características espaciais e temporais da reorganização do movimento. Contudo, essa influência ocorreu somente no fim de uma série de tentativas. Este resultado, em conjunto com a ausência de diferença em aspectos cinemáticos e de desempenho entre os grupos experimentais, sugere que a expectativa de deslocamento futuro do alvo foi criada em função das tentativas iniciais de uma série e não pela informação verbal / The aim of the present study was to evaluate the effect of expectancy on reorganization of spatial and temporal dimensions in interceptive actions. The study was conducted through two experiments in which participants were to manually intercept a virtual moving target with different probabilities of target trajectory/velocity shift. Comparison between a group that received verbal information concerning probability of target trajectory/velocity shift (PR), and another group that did not receive that information (SI) was made in both experiments. Results of the experiment on target trajectory shift showed that, in addition to gradual movement reorganization in the spatial dimension, interceptive actions were controlled by a predictive mechanism which seemed to be continuously updated by visual information. Of main interest, it was shown that in both experiments probability of target trajectory/velocity change influenced the spatial and temporal characteristics of movement reorganization. However, this influence occurred only at the end of a series of trials. The same effect was observed in the experiment on target velocity shift. This result, adjoined with the absence of difference in kinematic and performance aspects between experimental groups, suggests that expectancy about future target displacement was created by the initial trials of a series and not by verbal information on probability of target trajectory/velocity shift

Durante diferentes atividades cotidianas ou esportivas o ser humano é submetido a desafios unilaterais que podem estar relacionados à performance de uma tarefa específica ou a própria manutenção de sua postura. Portanto, é natural o desenvolvimento motor de um membro em relação ao outro para tarefas específicas, desde que estas sejam repetidas de forma não simétrica. Desta forma, pode-se supor que sujeitos que possuam maiores estresses físicos unilaterais apresentem maior probabilidade em desenvolver assimetrias funcionais e morfológicas. O presente trabalho apresenta três diferentes experimentos visando investigar as assimetrias funcionais e morfológicas relacionadas ao controle de movimento para tarefas dinâmicas e estáticas em diferentes condições e grupos. O primeiro experimento visou investigar as diferenças, entre os membros inferiores, no controle de movimento entre sedentários e atletas, utilizando para isto a postura ereta quieta e o salto com contra-movimento nas condições bipedais e unipedais. O segundo experimento visou investigar o efeito da fadiga neuromuscular unilateral e bilateral no controle de movimento, entre membros, durante o salto com contra-movimento e a postura ereta quieta bipedal. O terceiro experimento objetivou investigar o efeito prolongado da temporada esportiva no controle de movimento, entre membros, de atletas, utilizando o salto com contra-movimento e a postura ereta quieta nas condições unipedal e bipedal. Inicialmente, o presente trabalho concluiu que não parece existir relação entre as diferenças antropométricas e funcionais. Indivíduos sedentários e atletas possuem diferenças entre os membros inferiores, entretanto supõe-se que os mecanismos relacionados à tais fenômenos não sejam os mesmos, como no caso dos sedentários, onde as assimetrias poderiam estar relacionadas ao pobre controle de força, sinergismo e padrão de coordenação.. Analisando as diferenças entre sedentários e atletas foram observadas semelhanças em relação ao nível de assimetria para algumas variáveis analisadas. Deve-se considerar que os atletas analisados estavam no início da temporada esportiva, e possivelmente sem grande influência dos efeitos do treinamento prolongado. Para testar a hipótese do efeito prolongado, o terceiro experimento foi realizado e observou-se que a temporada esportiva não afetou todas as variáveis relacionadas ao controle de movimento estático e dinâmico em atletas e os maiores efeitos foram verificados durante as tarefas bipedais. Além disto, a fadiga neuromuscular também influenciou o controle de movimento em sedentários, produzindo ajustes compensatórios em algumas variáveis, principalmente nos ângulos articulares. Entretanto, as assimetrias previamente observadas não parecem serem alteradas durante as diferentes condições de fadiga neuromuscular. Para a tarefa dinâmica bipedal, observou-se que para todas as variáveis analisadas (ângulos articulares, parâmetros de desempenho e atividade muscular) apresentaram assimetrias. Curiosamente, se observa tendência à maior ativação do membro contra-lateral em função do membro fatigado. Portanto, o presente estudo ressalta o efeito do nível de condicionamento, o efeito da fadiga e do treinamento prolongado no controle de movimento dos membros inferiores em tarefas com diferentes demandas motoras bipedais e unipedais / The human body is exposed to different unilateral challenges during different daily and sportive tasks. These challenges may either be related to specific-task performance or posture maintenance. Thus, it is natural the increase of motor control in one limb related to another during specific tasks and movements. It can be assumed that individuals exposed to higher physical unilateral stress show greater probability to develop functional and morphological asymmetries. The present study shows three different experiments in order to investigate the functional and morphological asymmetries related to the motor control for dynamic and static tasks in different conditions and groups. The first experiment aimed to investigate the differences between the lower limbs, related to the motor control between sedentary and athletes during two tasks: quiet stance and countermovement jump in bi- and unipedal conditions. The second experiment aimed to investigate the effect of neuromuscular fatigue on uni- and bilateral tasks related to the motor control between lower limbs during both double-leg tasks: countermovement jump and quiet stance. The third experiment aimed to investigate the effect of prolonged sportive season in motor control, between lower limbs, during two tasks: quiet stance and countermovement jump in bi- and unipedal conditions. We concluded that there was no correlation between the anthropometric and functional asymmetries. Both sedentary and athlete groups had differences between the lower limbs in several variables, however it is assumed that the mechanisms related to such phenomena are not the same. There were similarities between sedentary and athlete groups related to the level of asymmetry for some variables. We must consider that the athletes were analyzed at the beginning of the sportive season, without the training influence. To verify the prolonged effect hypothesis, the third experiment was conducted and it was observed that the sportive season did not affect all the variables related to the motor control and the greatest effects were observed during the bipedal tasks. In addition to that, the neuromuscular fatigue influenced the control of movement in the sedentary group, showing compensatory adjustments in some variables, especially in the maximal joint angles. However, we observed that the asymmetries did not change during different neuromuscular fatigue conditions. During the bipedal dynamic task it was observed asymmetries in all variables (joint angles, performance parameters and muscle activity). Interestingly, it was also observed the trend to higher activation of the contra-lateral lower limb during the fatigued limb. So, this study highlights the effect of the conditioning levels, the neuromuscular fatigue effect and the prolonged training to the motor control of the lower limbs in different tasks and conditions

O Sistema Nervoso é capaz de organizar, controlar e adequar respostas motoras diante de mudanças repentinas no ambiente. No esporte tal capacidade é solicitada frequentemente. A cobrança do pênalti no futebol é um exemplo interessante deste tipo de situação, pois exige do atleta a tomada de decisão do lado para o qual chutar. Porém, muitas vezes esta decisão é executada sobre a influência de vários fatores que afetam o desempenho no decorrer de uma partida no futebol, entre eles a fadiga. Com o objetivo de estudar o efeito de fadiga sobre o desempenho em uma tarefa de computador que simula alguns aspectos da cobrança de um pênalti no futebol, foram comparadas duas situações: controle e de fadiga muscular promovida por um sistema de alavanca com sobrecarga. Os voluntários permaneciam sentados em frente ao monitor de um computador que apresentava três pontos que representavam o cobrador, a bola e o goleiro. O goleiro poderia deslocar-se tanto para a direita como para a esquerda (aleatoriamente) em momentos diferentes. A tarefa do voluntário era a de inclinar uma alavanca no exato momento em que o cobrador, se deslocando em direção a bola, coincidisse com este último, e se possível a alavanca deveria ser inclinada na direção oposta ao movimento do goleiro. Os resultados indicaram um melhor desempenho no percentual de respostas com lateralidade correta e uma menor variabilidade (respostas demasiadamente antecipadas ou atrasadas) dos voluntários na condição controle do que em condição de fadiga. / The Nervous System is capable of organizing, controlling and adjusting motor responses to sudden changes on the environment. In sports this ability is often tested. The penalty kick in soccer is an interesting example of this type of situation, because it requires of the kicker quick decision making as to which side to kick, depending on the last minute actions of the goalkeeper. However, often this decision influencedd by several factors which affect the performance during a soccer game, such as fatigue..In order to study the effect of fatigue on performance in a computer task which simulates some aspects of the penalty kick in soccer, two situations were compared: control and with fatigue, induced by a lever system with weights. Volunteers remained seated in front of a computer screen that presented three small circles, vertically aligned, which represented the kicker, the ball and the goalkeeper. At the beginning of each trial the kicker (lower circle) moved vertically up, at contant speed, toward the ball (middle circle) and at different times before kicker-ball contact the goalkeeper (upper circle) might move to the right or to the left, randomly. The task of participants was to incline a lever at the instant of kicker-ball superposition, and, if possible, to the side opposite to that of the goalkeeper\'s movement. Results indicated a slightly better performance in the percentage of trials with correct laterally, and lower temporal variability, with fewer delays or anticipations when participants were in the control rather than the fatigue condition.

A hanseniase e uma doenca endemica no Brasil sendo considerado um problema de saude publica. A hanseniase causa acometimentos oculares, cutaneos, sistemicos e nervosos, sendo este ultimo o mais importante, pois provoca alteracoes de sensibilidade e propriocepcao, que podem afetar o controle da postura. O objetivo principal deste estudo e descrever o controle postural de sujeitos portadores de hanseniase e compara-los com sujeitos saudaveis. Para tanto, tambem serao mensuradas algumas respostas sensorio-motoras possivelmente relacionadas ao controle postural destes sujeitos. Foi avaliado o controle postural por meio do Teste Clinico de Interacao Sensorial no Equilibrio modificado utilizando-se uma plataforma de forca e do BESTest, Balance Evaluation Systems Tests, uma medida funcional do equilibrio. Quanto as respostas sensorio-motoras, foram avaliados os reflexos tendinosos, a forca muscular, a palpacao de dois nervos do membro inferior, a propriocepcao, a sensibilidade cutanea, a acuidade visual, em todos os sujeitos, e o grau de incapacidades fisicas apenas nos sujeitos portadores de hanseniase. De forma geral, todas as respostas sensorio-motoras dos portadores de hanseniase estao prejudicadas. O desempenho no BESTest indica que os portadores de hanseniase apresentam dificuldades em controlar o equilibrio em tarefas tipicas das atividades da vida diaria. O desempenho nas tarefas de equilibrio quantificado pela posturografia indica que os portadores de hanseniase apresentam dificuldades em controlar o equilibrio na postura ereta quieta sem ou com manipulacao da informacao sensorial. Os resultados reportados neste trabalho mostram pela primeira vez que portadores de hanseniase possuem deficits no controle postural relevantes para a manutencao do equilibrio e para execucao de outras tarefas comuns da vida diaria. Estes resultados sugerem que portadores de hanseniase devem receber auxilio especial para que estes deficits possam ser diminuidos / Hansen\'s disease is an endemic disease in Brazil and it is considered a public health problem. The Hansen\'s disease causes eye, cutaneous, systemic, and nervous problems; being the latter the most important hence affects the sensibility and proprioception and possibly can affect postural control. The main goal of this study is to describe the postural control of individuals with Hansen\'s disease and compare them to healthy individuals. For such, it will also be measured sensory-motor responses possibly related to the postural control of these individuals. The postural control was evaluated employing a modified version of the Clinical Test of Sensory Interaction and Balance using a force plate and the BESTest, Balance Evaluation Systems Tests, a functional measure of the postural control. In regard to the sensory-motor responses, it was evaluated the tendinous reflex, muscle force, palpation of two nerves of the lower limb, proprioception, cutaneous sensibility, visual acuity, in all subjects, and the degree of physical incapacity only of individuals with Hansen\'s disease. In general, all the sensory-motor responses of the individuals with hanseniase are deteriorated. The performance in the BESTest suggests that individuals with Hansen\'s disease have problems in controlling their posture in typical daily living tasks. The performance in the postural control tasks measured by posturography also suggests that the individuals with Hansen\'s disease have problems in controlling their posture with or without the manipulation of the sensory information. These results show by the first time that individuals with Hansen\'s disease have significant postural control deficits that impair their ability to maintain their upright posture and to execute common daily living tasks. These results suggest that individuals with Hansen\'s disease must receive special attention in order to reduce these deficits

INTRODUCTION: Muscle activity and timing of the swing phases may contribute to the differences we see in athletes at different skill levels. The purpose of this study is to analyze the differences between mean muscle activity, peak muscle active and time to peak muscle activity for select muscles in the lower extremity as well as the differences between start times for swing phases and bat velocity prior to impact for a skilled and recreational group. METHODS: Twelve healthy subjects were split into two groups based on competitive level and analyzed hitting off of a tee. RESULTS: No significant differences were seen between muscle activity or the start time for the landing and swinging between groups. The skilled group did have a faster time to peak muscle activation for the front leg biceps femoris (p = 0.024), start the shifting (p = 0.12) and stepping (p = 0.11) phases significantly earlier as well as had a higher bat velocity prior to ball contact (p = 0.42) than the recreational group. CONCLUSION: Mean and peak muscle activity trends to be lower for skilled hitters than recreational hitters. Evidence of the skilled group starting the shifting and stepping phase earlier as well as having a higher bat velocity prior to impact could be important in separating hitters into skill level.

The ability to stop ongoing movements or prevent unwanted movements is fundamental to behavioural control. This thesis addresses the neural processes underlying inhibitory control and how initiation and stop processes interact to control behaviour. We conducted four studies, employing various behavioural tasks that require humans to prepare to initiate a response with the possibility that it may have to be prevented or stopped from being initiated. In the first experiment we sought to determine whether the increase in reaction time (RT) during the performance of traditional stop-signal task was due to a decreased the amount of go-related preparatory activation. We used a startling acoustic stimulus (SAS) to determine whether the go-response could be triggered involuntarily, and investigated whether the latency of SAS responses were delayed when participants were instructed that they might have to stop their response compared to when they knew they would never stop (i.e., simple RT task). We found that the go-response was prepared in advance during the stop-signal task, but to a lesser degree as indicated by the slower SAS response latency, compared to when go trials were completed in the simple RT task. Thus, even the possibility of having to stop a response reduces the level of preparatory go-activation. The second experiment tested the hypothesis that behavioural control during a stop-signal task is determined by an independent race between go- and stop-processes. In this experiment we used a SAS to manipulate initiation and inhibition by probing the go- and stop-response prior to and after the stop-signal respectively in a stop-signal task. We found that the go-response could be triggered by the SAS even 200 ms following the stop-signal suggesting that behavioural control during a stop-signal task is not determined by an independent race between go- and stop-activations, but rather by an interaction between go-activation and stop processes. The third experiment investigated the effect of advance preparation on the ability to proactively and selectively inhibit a single limb in a bimanual response that had been cued to maybe stop. TMS was used to measure the excitability of the limb that was cued to maybe stop in comparison to the limb that was to continue with its response. In addition, a SAS was used to probe the preparatory state of the go-response in each limb. We found that increased preparatory go-activation of responses in both limbs overshadowed the neurophysiological evidence of proactive selective inhibition, while processes related to the selective stopping task appeared to suppress subcortical motor structures and the ability of the SAS to involuntarily trigger the prepared responses. The fourth experiment sought to determine the role of the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (preSMA) in the inhibition of response initiation during a go/no-go task. We temporarily deactivated rIFG or preSMA using continuous theta burst stimulation (cTBS) and examined changes in inhibition, voluntary initiation, and the ability of a SAS to involuntary trigger the initiation of the response. We found that stimulation to both cortical sites impaired participant’s ability to withhold movements during no-go trials. Notably, deactivating rIFG and preSMA did not affect voluntary initiation and did not enable the SAS to involuntarily trigger the response. These findings implicate the rIFG and the preSMA in the ability to inhibit responses during a go/no-go task, and suggests that preparation and initiation of the go-response occurs in response to the imperative stimulus, with inhibition only applied once the stimulus is identified as a no-go signal. Taken together, these studies show that i) modulation of preparatory go-activation contributes to the ability to inhibit a motor response, ii) motor response inhibition is achieved by initiation activation being prevented from reaching threshold, iii) preparatory go-activation overshadows proactive inhibition, iv) inhibitory control depends on the integrity and recruitment of top-down inhibitory control to suppress initiation activation once a no-go stimulus is identified. This research speaks to the interaction between initiation and inhibition processes and provides novel insight and evidence in support of an interactive model of inhibitory control.

abstract: Fractal analyses examine variability in a time series to look for temporal structure or pattern that reveals the underlying processes of a complex system. Although fractal property has been found in many signals in biological systems, how it relates to behavioral performance and what it implies about the complex system under scrutiny are still open questions. In this series of experiments, fractal property, movement kinematics, and behavioral performance were measured on participants performing a reciprocal tapping task. In Experiment 1, the results indicated that the alpha value from detrended fluctuation analysis (DFA) reflected deteriorating performance when visual feedback delay was introduced into the reciprocal tapping task. This finding suggests that this fractal index is sensitive to performance level in a movement task. In Experiment 2, the sensitivity of DFA alpha to the coupling strength between sub-processes within a system was examined by manipulation of task space visibility. The results showed that DFA alpha was not influenced by disruption of subsystems coupling strength. In Experiment 3, the sensitivity of DFA alpha to the level of adaptivity in a system under constraints was examined. Manipulation of the level of adaptivity was not successful, leading to inconclusive results to this question. / Dissertation/Thesis / Masters Thesis Psychology 2019